The present invention relates to a power converter for carrying out a control by switching operation and a system using the same.
A power converter controlled by switching operation is used in various apparatus of motor driving apparatus or the like and a function requested thereto becomes severe. In order to meet the needs, a switching characteristic of a power element constituting a power converter is improved and a switching period is considerably accelerated to 10 ns through 100 ns. Therefore, a frequency of EMI (electromagnetic interference) noise generated from a system using a power converter is increased and is liable to invade other electronic apparatus, information communicating apparatus or the like as common mode noise via a stray capacitance and electromagnetic hazard is liable to generate.
A common mode current (leakage current) flowing in a motor driving system is made to flow via a stray capacitance distributed in the system in various states. In order to restrain the common mode current, a circuit model grasping a behavior of the common mode noise (voltage, current) of the driving system and reflecting the behavior becomes indispensable.
FIG. 11 is a diagram showing an outline constitution of a motor driving system which is an example of a system using a power converter controlled by switching operation. The motor driving system of FIG. 11 includes an alternating current power source 1, an AC reactor 2, a power converter 3, and a motor 4. Further, ground lines (not illustrated) of the AC reactor 2, a frame (not illustrated) of the motor 4 and the power converter 3 are connected to a ground 5. Further, here, the frame indicates a structural member supporting an apparatus covered with a total of the apparatus by a conductor in a state of being electrically insulated from a conductive portion of an apparatus.
The power converter 3 is supplied with a power source from the alternating current power source 1 via the AC reactor 2 to convert into a power source having an arbitrary frequency and an arbitrary voltage. The power converter 3 constitutes basic constituent elements by a converter (forward converter) 31 for converting the inputted alternating current power source into a direct current voltage, a smoothing capacitor 32 for smoothing the direct current voltage outputted from the converter 31, and an inverter (inverse converter) for converting the smoothed direct current voltage into an alternating current voltage, the elements are mounted to a wiring board 30, and the converter 31 and an inverter 33 are connected via direct current main circuit conductors (direct current buses) 300n, 300p formed at the wiring board 30. Further, an element case or the like constituting the converter 31 and the inverter 33 is attached with a cooling fin 34. The cooling fin 34 is for restraining temperature rise of the elements or the like and electrically connected to a ground (not illustrated in FIG. 11) of the wiring board 30.
There are two kinds of EMI noises in such a system. One of them is a normal mode noise (differential mode noise) generated by a differential voltage from the direct current main circuit conductors 300n, 300p between the converter 31 and the inverter 33 and other thereof is a common mode noise generated by the common mode current flowing via parasitic capacitances distributed in the motor driving system. The normal mode noise gives rise to the common mode noise and in order to reduce the EMI noise, it is important to control the normal mode noise.
As shown by FIG. 11, there are present three kinds of the common mode current of a current Ic 2 leaked from the element case or the like of the power converter 3 to the ground via the cooling fin 34, a current Ic 3 leaked to the ground via the frame of the AC reactor 2 and a current Ic 1 leaked via the motor frame. As shown by FIG. 11, the common mode current is made to flow via the stray capacitance and therefore, a noise component at a high frequency is made to flow as a leakage current. Further, in FIG. 11, notation with regard to the stray capacitance is omitted.
The inventors have proposed a technology of reducing a common mode current flowing via a stray capacitance distributed at inside of a system (refer to Nonpatent Reference 1, Patent Reference 1). According to the system, damping impedances are inserted between a single or a plurality of elements in elements constituting the system and the ground.
The normal mode noise can be restrained by inserting a noise filter to a direct current line between a converter and an inverter. However, there is a possibility of newly forming a current path inducing the common mode noise via an apparatus added for a countermeasure thereagainst and it is preferable to avoid an additional circuit for reducing the normal mode noise as less as possible.
The inventors have proposed also a technology of reducing the normal mode noise (refer to Nonpatent Reference 1, Patent Reference 1). According to the technology, direct current main circuit conductors between a converter and an inverter are arranged at wiring layers of a multilayer wiring board different from each other at symmetrical positions by interposing insulating layers therebetween.
FIG. 12 shows an outline constitution of an example of the wiring board 30 utilized in the power converter 3 shown in FIG. 11 (also similar to the power converter 3 shown in Nonpatent Reference 1). The wiring board 30 includes 4 layers of wiring layers from a first wiring layer (not illustrated) to a fourth wiring layer 364, and insulator layers 372 through 374 are arranged among the respective wiring layers and surfaces of the first wiring layer and the fourth wiring layer 364 (illustration of the insulator layers at the surface of the first wiring layer and between the first wiring layer and the second wiring layer 362 is omitted).
The first wiring layer (not illustrated) is a layer mainly provided with a gate circuit of the power converter 3, wirings for a voltage detector, a current detector, a wiring for transmission for supplying a power source and the like. The second wiring layer 362 is provided with a first positive side direct current wiring 301p and a second positive side direct current wiring 302p constituting the direct current bus 300p. The third wiring layer 363 is provided with a negative side direct current wiring 301n constituting the direct current bus 300n. Further, the first positive side direct current wiring 301p and the second positive side direct current wiring 302p are connected via an electromagnetic relay 35. When it is not necessary to cut conduction between the converter 31 and the inverter 33, the electromagnetic relay 35 can be omitted by constituting a single wiring by connecting the first positive side direct current wiring 301p and the second positive side direct current wiring 302p. Further, the fourth wiring layer 364 is a wiring layer formed with a ground wiring 304 constituting a ground face of the power converter 3. Further, only portions of the wiring board 30 at vicinities of wirings constituting the direct current paths 300p, 300n are shown in the wiring board 30 of FIG. 12.
The converter 31 and the inverter 33 constituted by IMP are respectively arranged at a converter arranging region 31S and an inverter arranging region 33S. Further, an output terminal of the converter 31 is connected to one end of the first positive side direct current wiring 301p and one end of the negative side direct current wiring 301n and an input terminal of the inverter 33 is connected to one end of the second positive side direct current wiring 302p and other end of the negative side direct current wiring 301n. Further, the smoothing capacitor 32 is connected to a middle point of the second positive side direct current wiring 302p and a middle point of the negative side direct current wiring 301n in correspondence therewith.
A differential mode voltage ΔV between the direct current paths 300p, 300n becomes ΔV=(Ls1+Ls2−2M) di1/dt=Leffdi1/dt when a self-inductance of direct current bus 300p is designated by notation Ls1, a self-inductance of the direct current bus 300n is designated by notation Ls2, a mutual inductance thereof is designated by notation M, an effective inductance thereof is designated by notation Leff and a current flowing in the direct current bus 300p is designated by notation i1. The voltage ΔV is reduced by reducing the effective inductance Leff, that is, by increasing the mutual inductance M.
According to the wiring board 30 of FIG. 12, the first positive side direct current wiring 301p and the second positive side direct current wiring 302p and the negative side direct current wiring 301n constituting the direct current buses 300p, 300n are provided with structures symmetrical with each other by interposing the insulator layer 372 and therefore, the mutual inductance M is increased and the differential mode voltage ΔV can be reduced. Therefore, the differential mode current is reduced and the common mode current accompanied thereby can also be reduced.
However, a current at a frequency bond equal to or higher than several MHz constituting a noise current is diffused and propagated at a surface of the conductor by a skin effect and therefore, in the case of a high frequency current flowing in the direct current buses 300p, 300n by switching operation of the power converter, not only a conducting EMI noise but also a radiating EMI noise pose a problem. Further, the elements constituting the power converter are constituted by three-dimensional structures and therefore, such a radiating noise is easily propagated via stray capacitances among the respective elements and a countermeasure thereagainst is becoming difficult. A concentrated constant filter of a background art cannot control an EMI noise diffused on a surface of a power transmission line.
[Nonpatent Reference 1]
Nobuyoshi Mutoh, Mitsukatsu Ogata, Kayhan Gulez, and Fumio Harashima “New methods to Suppress EMI Noises in the Motor Drive System”, distributed in the “9th European Conference on Power Electronics and Applications” held at a Gratz, Austria on Aug. 27 through 29, 2001 in the form of CD-ROM (ISBN: 90-75815-06-9)
[Patent Reference 1]
Japanese Patent Publication No. 3432505